Any reasonable IS mount rear brakes?

I have an older Black Sheep frame lying around that I was planning on converting to SS. It has vertical drops, so I was planning to use White Industries eccentric ENO hubs to tension the chain. However, my frame has IS mounts on the chain stays (I think this is to allow racks to be mounted on the frame), and I don't think there is enough room to accommodate the adjustable post mount converters that come with the ENO hubs. So I'll have to go a different route on wheels.

I'm wondering if there are any reasonable IS mount rear brakes out there. Looks like Magura makes them, but they are $$$ (My original plan was to use BB7's). Any other thoughts?

Hope Minis (two-piece caliper) or Mono Minis are available in IS for a 140mm (caliper No.5) or 160mm rear (No.3). They're both relatively inexpensive on eBay nowadays, especially since the new Tech systems came out. Both brakes use the same fully serviceable lever. The calipers are also easily maintained/overhauled as they use the same piston seals found on the Mono Minis up until 2008.